In many countries it is a recommended practice to illuminate vehicle headlamps when driving on the highway during daylight hours. Most "automatic on" headlight devices of the prior art derive their power from the vehicle battery, and include an automatic switch in parallel to the manual switch normally provided for controlling the headlamps. The automatic switch in one form thereof is conditioned to ON by means which is responsive to a voltage at the battery terminals above a threshold value. Accordingly, different devices will normally be required according to the distribution voltage of the vehicle system. In another form of automatic switch this is conditioned to ON by means which is responsive to a voltage at the ignition coil of the vehicle. Where the power reserve of the battery is low or becomes low, the foregoing devices will result in an undesirable drain.
In U.S. Pat. No. 4,323,837 there is described a power supply arrangement for vehicles including a generator (which term as is used herein includes dynamos and alternators or the like) driven by the engine of the vehicle and a battery, wherein the output of the generator is connected to the battery through a diode serving to pass a charging current to the battery and block the flow of current in a reverse direction. Essential loads such as the vehicle ignition are connected to the battery and powered thereby, whereas non-essential loads which may include lamps are connected to the generator output and derive their power solely therefrom.
The output of the generator is governed primarily by a voltage regulator. Certain regulators require the presence of a threshold voltage at the generator output terminal in order to condition the generator to provide a full, regulated output. Such threshold voltage is normally provided by the battery, or where the battery is discharged or effectively disconnected by a blocking diode, for example, it may be provided by the generator itself, relying on weak residual magnetic fields normally present therein. However, if a heavy electrical load is permanently connected to the generator output, this may prevent the necessary attainment of the threshold voltage.
Where the load circuit is powered solely from the generator output, the power available to the load circuit will be somewhat dependent upon the engine speed of the vehicle. Where the load is a headlamp, the light output may be insufficient under certain conditions, and pose a safety hazard. While in the foregoing patent a servo mechanism is described to overcome this, additional circuitry is required which would preclude the load from being directly connected to the generator output.
It is desired on occasion to provide a booster charge for a battery of another vehicle. Where the batteries are directly interconnected using booster cables or the like, a high and uncontrolled current may be drawn from the source battery, which may result in damage.
It is an object of my invention to provide an automatic on switch that is relatively insensitive to the distribution voltage of the vehicle.
It is another object of my invention to provide an automatic on switch the output of which may be permanently connected to the load and yet which will not prevent the generator being conditioned to provide its full output.
It is still another object of my invention to provide an automatic on switch in accordance with the foregoing objects that may be connected in parallel with a manual switch therefor to optionally connect the load to a battery.
It is a further object of my invention to provide an automatic on switch in accordance with the foregoing objects that is simple and economically produced.
It is yet another object of my invention to provide a device to facilitate booster charging of another battery not normally connected to the power supply system of the vehicle, while protecting the battery thereof.